To determine the impact of an experimental intervention on aging, it is essential that an investigator have knowledge of how the intervention alters the pathological lesions that occur with age. Age-related pathology increases exponentially with advancing age and is largely responsible for age-related morbidity as well as mortality. Pathological information also provides investigators with insight into the potential biological/molecular mechanism(s) of the intervention. Furthermore, the pathological assessment of old animals that are included in basic studies of biological aging processes is necessary to help investigators determine whether the changes in physiological/biochemical parameters measured are associated with or are independent of underlying pathological conditions. Thus it is essential to obtain accurate and thorough pathological assessments of aging animals. The Pathology Core will provide investigators in the three Projects with detailed end-of-life pathological analyses of the lesions that occur with age in colonies of tissue-specific (liver, skeletal muscle and white adipose tissue [WAT]) GHRKO mice . The Pathology Core will also provide investigators in the four Projects with cross-sectional pathological analyses of the specific tissues obtained from Ames dwarf, GHRKO and tissue-specific GHRKO mice. The Specific Aims of the Pathology Core are as follows: Aim 1: To conduct comprehensive pathological analyses of the genetically manipulated mice and their wild- type littermates that die spontaneously or are in the moribund category in the aging colonies. Aim 2: To conduct cross-sectional histopathological analyses of tissues obtained from genetically manipulated mice and their littermates. These data will allow investigators to evaluate the effect of the genetic manipulations on the histological changes in specific tissues at specific age. RELEVANCE (See instructions):